1. Field of the Invention
The present invention relates to a synchronism judgment apparatus for judging whether frame synchronization has been established in a transmission system in which frame synchronization with respect to frames as a sequence of slots to which sync patterns are distributed according to the sync patterns, as well as to a communication system where such a synchronism judgment apparatus is applied.
2. Description of the Related Art
Conventionally, in the field of mobile communication, various systems have been constructed in order to deal with differences in transmission information, communication form, service to be provided, etc. And extensive researches and developments have been made to exploit new technologies.
Among those technologies, the CDMA (code division multiple access) is applied positively to next-generation mobile communication systems as a promising wide-band multiple access method because it offers a high degree of confidentiality, has such properties that a communication is less affected by interference/disturbance and fluctuations such as frequency selective fading in radio transmission channel, and enables flexible adaptation to differences of the above kind.
FIG. 10 shows the configuration of an exemplary receiving part that is provided in a radio base station of a CDMA mobile communication system.
As shown in FIG. 10, two reception waves I and Q that were subjected in parallel to spreading processing with orthogonal spreading codes in a transmitting end and have occupied bands in a prescribed band (for simplicity, it is assumed here to be a baseband) are supplied to a despreading processing part 61 in parallel. The two outputs of the despreading part 61 are connected to the respective inputs of a detector circuit 62. Demodulation signals i and q corresponding to the two respective reception waves I and Q are obtained at the two outputs of the detector circuit 62. The monitoring output and the first to third control outputs of the detector circuit 62 are connected to the first to fourth inputs of a synchronism judgment circuit 70, respectively. The number of bits Nb (described later) is supplied externally to the fifth input of the synchronism judgment circuit 70. A synchronism judgment signal is output to the output of the synchronism judgment circuit 70.
The synchronism judgment circuit 70 is composed of the following components:
A memory 71 in which known sync pattern (hereinafter referred to as xe2x80x9creference bit stringxe2x80x9d) to be received are stored in advance.
A comparator gate 72 having two inputs that are connected to the output of the memory 71 and the monitoring output of the detector circuit 62, respectively.
An AND gate 73 having two inputs that are connected to the output of the comparator 72 and the first control output of the detector circuit 62.
A counter 74 having an enable terminal EN to which the output of the AND gate 73 is connected and a clock terminal CLK and a reset terminal RESET to which the second and third outputs of the detector circuit 62 are connected, respectively.
A comparator 75 having one input to which the output of the counter 74 is connected and the other input to which the number of bits Nb is supplied.
A flip-flop 76 having a clock terminal CLK that is connected to the second output of the detector circuit 62 together with the clock terminal CLK of the counter 74 and a D input that is connected to the third output of the detector circuit 62 together with the reset terminal RESET of the counter 74.
A flip-flop 77 provided at the final stage and having a D input that is connected to the output of the comparator 75 and a clock terminal CLK that is directly connected to the non-inverting output Q of the flip-flop 76.
In the conventional example having the above configuration, so that processing for realizing a transmission power control and setting and updating of a variety of transmission rates and transmission forms that are suitable for channel allocation, zone configuration, etc. can be performed repeatedly in time series at a prescribed cycle in each of a mobile station and the radio base station, of the above-mentioned reception waves I and Q, the reception wave Q that is received through a control channel (DPCCH) used for transmission of control information from the mobile station to the radio base station according to a channel control is given as a reception wave that is modulated with a sequence of frames (slots) described below.
As shown in FIG. 11A, each slot is composed of four fields containing the following information. The word length of each slot is 10 bits (corresponding to 2,560 chip cycles) irrespective of the values of those fields.
xe2x80x9cPilot bitsxe2x80x9d to be used as a sync pattern.
xe2x80x9cTFCI bitsxe2x80x9d indicating a communication speed.
xe2x80x9cFBI bitsxe2x80x9d to be used for controlling transmission diversity for a downlink.
xe2x80x9cTPC bitsxe2x80x9d indicating the form of transmission power control to be performed for a downlink.
As shown further in FIG. 11, each frame is configured in such a manner that 15 slots (in the maximum case) as described above are packed in order of time series. The length of each frame is 10 ms irrespective of the number of slots actually packed.
As shown in FIG. 12, the xe2x80x9cpilot bitsxe2x80x9d field accommodates a known bit string (hereinafter referred to as xe2x80x9csync patternxe2x80x9d) that has a word length of 3 to 8 bits and varies depending on a xe2x80x9cslot numberxe2x80x9d that indicates a packing position of the associated slot in the frame.
Among the bits that constitute each sync pattern, bits that are halftone-dot-meshed in FIG. 12 will be referred to below simply as xe2x80x9cFSW (frame sync-word) bits.xe2x80x9d
The despreading processing part 61 performs despreading processing on the above-mentioned reception waves I and Q in parallel. The detector circuit 62 outputs the following demodulation signals i and q by demodulating in parallel two signals obtained by the despreading.
A demodulation signal i indicating, in the form of a sequence of prescribed frames, transmission information (corresponding to a speech signal or the like) received through a data channel (DPDCH).
A demodulation signal q indicating, in the form of a sequence of frames as described above (see FIG. 11), control information received through a control channel (DPCCH; mentioned above).
In the demodulation processing that is performed in the detector circuit 62 to generate those demodulation signals i and q, phase rotation that has occurred in an upstream radio transmission path from a mobile station to the radio base station is corrected. However, the procedure of such demodulation processing is not an essential feature of the invention and can be realized by using various known technologies, and hence will not be described.
Since the bit string obtained as a demodulation signal q by the above demodulation processing is bit-synchronized with the reception wave Q, the detector circuit 62 performs the following processing by operating independently to divide the bit string according to the above-described frame configuration.
Extracting a bit string that can be regarded as a frame (hereinafter referred to as xe2x80x9cinterim framexe2x80x9d because it does not necessarily coincide with a true frame) by operating independently to divide the above-mentioned bit string into parts each having the above-mentioned frame word length.
Extracting partial bit strings each of which can be regarded as a sync pattern from the bit string constituting the interim frame according to the frame configuration shown in FIG. 11B and FIG. 12. It is assumed that the number of bits included in such a partial bit string conforms to and is proportional to the actual word length (3 to 8 bits) of a sync pattern.
Generating a frame clock signal that rises at the head of the interim frame and a slot enable signal that is an NRZ signal whose logical value becomes xe2x80x9c1xe2x80x9d only in the periods of valid slots included in the interim frame.
The known bit strings (see FIG. 12; hereinafter referred to as xe2x80x9creference bit stringsxe2x80x9d) to be received as pilot bit strings of slots that are packed in each frame in a state that frame synchronization is established are stored in advance in the memory 71 of the synchronism judgment circuit 70.
The comparator 72 judges, sequentially, bit by bit, whether each of partial bit strings (see parts (a) of FIG. 13) is the same as a reference bit string (see parts (b) of FIG. 13) stored in the memory 71, and outputs binary information indicating a result of the judgment.
The AND gate 73 supplies the counter 74 with a judgment signal (see parts (d) of FIG. 13) that consists of bit strings corresponding to respective valid slots that are indicated by the above-mentioned slot enable signal (see parts (c) of FIG. 13).
The counter 74 is reset at the end of each interim frame according to the frame clock signal. By sampling and recognizing the logical values of the judgment signal in synchronism with the clock signal, the counter 74 counts, for each interim frame cycle, the number of times the result of the judgment performed by the comparator 72 is xe2x80x9cfalsexe2x80x9d for only valid slots.
The comparator 75 judges whether the above number of times (see parts (e) of FIG. 13) is less than or equal to the number of bits Nb given as a fixed number as mentioned above (see parts (f) of FIG. 13), and outputs a synchronism judgment signal (see parts (g) of FIG. 13) indicating a result of the judgment.
The flip-flop 77 samples the synchronism judgment signal at the leading edge (or trailing edge) of the frame clock signal that is synchronized with the clock signal by the flip-flop 76, and outputs it.
Therefore, establishment of or pulling out of frame synchronization is properly judged as long as the number of bits Nb is a proper value, and hunting, backward alignment guard, and forward alignment guard that are necessary for establishment and maintaining of frame synchronization can be performed smoothly based on a result of the synchronism judgment.
In the above conventional example, all sync patterns that are distributed to respective slots are collated with the known reference bit strings.
However, for example, the collation may be performed for only FSW bits (mentioned above) that are included in sync patterns in a manner shown in FIG. 14B.
Incidentally, in the above conventional example, the number of bits Nb is set at a fixed value though the number of valid slots that are packed in each frame is smaller than 15 in the following two modes:
A burst receiving mode in which frames that are transmitted intermittently from a mobile station where a certain call (including a call for location registration) occurred and each of which is a sequence of slots indicating control information are to be received.
A compressed mode in which transmission information that is transmitted in compressed form are to be received in order to access in parallel a TDMA mobile communication system and a wide-band CDMA mobile communication system by sharing a single frequency synthesizer in dual mode mobile station.
That is, although the ratio of the number of bits Nb to the number of valid slots is proper in a continuous receiving mode in which the number of valid slots that are packed in each frame is always equal to 15, it becomes an unduly large value in the above burst receiving mode and compressed mode.
Therefore, in the burst receiving mode and the compressed mode, even when the reception wave Q does not vary in quality, the channel control may not be necessarily performed properly since the judgment standard of establishment of frame synchronization is alleviated and the accuracy of the above judgment and the service quality is lowered.
An object of the present invention is to provide a synchronism judgment apparatus and a communication system which enables a proper synchronism judgment while flexibly adapting to various configurations of frames transmitted via a radio transmission path.
Another object of the invention is to adapt to each receiving mode with flexibility and judge whether frame synchronization has been established with accuracy compared to the conventional art.
Another object of the invention is to identify a receiving mode with correctness and accuracy without the need for judging regularity or validity of each slot included in each frame.
Another object of the invention is to identify a receiving mode properly or accurately without the need for judging regularity or validity of each slot included in each frame as long as a channel control procedure is properly performed and an operand to be referred to during the course of the channel control is given with high reliability.
Another object of the invention is to flexibly and accurately judge whether frame synchronization has been established according to a threshold value suitable for the substantial number of valid slots even in a case where the number of valid slots included in each frame may vary due to a difference of receiving modes or a deterioration in the transmission quality of a transmission path.
Another object of the invention is to enable adaptation to a variety of permutations of slots that can be included in each frame.
Still another object of the invention is to realize a reduction in hardware scale as the smaller the ratio of a possible maximum threshold value to a possible minimum threshold value becomes and the greater values to be used as threshold values become, compared to a case where the threshold values to be used in all receiving modes are to be given directly and individually.
Yet another object of the invention is to judge establishment of frame synchronization with flexibility and accuracy by using threshold values suitable for individual frame configurations and the number of slots even in a case where the word length of a slot or the number of bits in each of sync patterns distributed to slots is not constant.
A further object of the invention is to judge establishment of frame synchronization with flexibility and accuracy as long as the word length of a slot and the number of bits in each of sync patterns distributed to slots are identified under the above channel control even when the word length or the number of bits is not constant.
Another object of the invention is to easily perform a synchronism judgment adapted to each receiving mode unless the number of receiving modes or the number of slots that can be included in a frame received in each receiving mode is changed.
Another object of the invention is to independently judge establishment of frame synchronization at high speed even where threshold values to be used in all receiving modes are not necessarily given externally in a steady manner.
Another object of the invention is to reduce the sum of information amounts of threshold values to be used in all receiving modes including a prescribed receiving mode as the range of threshold values becomes smaller, irrespective of the total number of receiving modes.
Another object of the invention is to independently judge establishment of frame synchronization at high speed even where differences between threshold values to be used in receiving modes other than a prescribed receiving mode and a reference threshold value to be used as a threshold value in the prescribed receiving mode are not necessarily given externally in a steady manner.
Another object of the invention is to reduce the sum of information amounts of threshold values to be used in all receiving modes as the range of the threshold values becomes smaller, irrespective of the total number of receiving modes to be dealt with.
Another object of the invention is to independently judge establishment of frame synchronization at high speed even where ratios between threshold values to be used in receiving modes other than a prescribed receiving mode and a reference threshold value to be used as a threshold value in the prescribed receiving mode are not necessarily given externally in a steady manner.
Still another object of the invention is to enable flexible adaptation to various requirements relating to maintenance and operation.
Yet another object of the invention is to enable flexible adaptation to a variety of forms of receiving modes and permutations of valid slots that can be included in a frame to be received in each of the receiving modes.
A further object of the invention is to maintain high transmission quality and service quality and enable flexible adaptation to a variety of communication services and transmission rates, and the transmission information amount that may vary to a large extent in a communication system to which the invention is applied.
The above objects are achieved by a synchronism judgment apparatus where establishment of frame synchronization is judged on every frame received, by comparing magnitude of values between a threshold value and the number of error bits in bit strings that constitute sync patterns of consecutive slots to be included as a sequence in the frame concerned. A suitable receiving mode is identified from a normal receiving mode in which a frame as a sequence of consecutive slots in time series is received and a specific receiving mode in which a frame as a sequence of slots transmitted intermittently in time series is received. The threshold value is set smaller when the identified receiving mode is the specific receiving mode than when it is the normal receiving mode.
In the synchronism judgment apparatus, the smaller the number of slots that are or can be included in the frame becomes, the smaller the allowable number of error bits in sync patterns that are distributed to the slots is set.
The above objects are achieved by a synchronism judgment apparatus where the specific receiving mode may be a plurality of specific receiving modes in which frames having a different number of slots from each other are respectively received.
In the synchronism judgment apparatus, even when there are a plurality of specific receiving modes different from the normal receiving mode, the smaller the number of slots included in a frame received in a specific receiving mode becomes, the smaller the threshold value used as a reference in judging establishment of frame synchronization is set.
The above objects are attained by a communication system where threshold values to be used for identifying the above-mentioned normal receiving mode and specific receiving mode are given in advance; the establishment of frame synchronization is judged by comparing magnitude of values between a threshold value to be used for a desired receiving mode among the given threshold values and the number of bits having different values in a sync pattern of the desired receiving mode, compared to a value of an actually received sync pattern.
In the synchronism judgment apparatus, the smaller the number of slots that are or can be included in the frame becomes, the smaller the allowable number of error bits in sync patterns that are distributed to the slots is set.
The above objects are achieved by a communication system where the small value is a product or an approximate value of the product of the reference threshold value to be used in the normal receiving mode and a ratio between the number of slots included in a frame to be received in the specific receiving mode and the number of slots included in a frame to be received in the normal receiving mode.
In the communication system, a threshold value to be used in a receiving mode other than the prescribed receiving mode is given as a ratio signifying relative magnitude with respect to the threshold value to be used in the prescribed receiving mode.
The above objects are attained by a communication system where the normal receiving mode and the specific receiving mode are discriminated from each other according to differences in the configurations of frames received.
In this communication system, the receiving mode is identified properly or accurately without the need for judging regularity or validity of each slot included in the frame concerned as long as the value of a field with the above-mentioned configuration, among the fields of individual frames, is referred to with high reliability during the process of a prescribed communication control.
The above objects are achieved by a communication system where the normal receiving mode and the specific receiving mode are discriminated from each other based on a channel control procedure.
In the communication system, the receiving mode is identified properly or accurately without the need for judging regularity or validity of individual slots included in each frame as long as the channel control procedure is properly performed and an operand to be referred to during the process of the channel control is given with high reliability.
The above objects are attained by a communication system where the normal receiving mode and the specific receiving mode are discriminated from each other according to the number of valid slots actually included in a frame received.
In the communication system, it is possible to flexibly and accurately judge establishment of frame synchronization according to a threshold value suitable for a substantial value of the number of valid slots even in a case where the number of valid slots included in each frame may vary due to a difference of receiving modes or a deterioration in the transmission quality of a transmission path.
The above objects are achieved by a communication system where the normal receiving mode and the specific receiving mode are discriminated from each other according to the configurations of frames received and the number of slots actually included in the frame.
In the communication system, the receiving mode is identified according to not only the number of slots included in each received frame but also its configuration.
The above objects are realized by a communication system where the normal receiving mode and the specific receiving mode are discriminated from each other based on a channel control procedure and the number of valid slots actually included in the frame.
In the communication system, a threshold value to be used for judging establishment of frame synchronization is given according to not only the number of slots included in each received frame but also a channel control procedure.
The above objects are realized by a communication system where threshold values respectively suitable for the normal receiving mode and the specific receiving mode are given in advance and one of the threshold values which corresponds to the identified receiving mode is used.
In the communication system, a threshold value to be used for any of receiving modes is obtained without performing any special calculation.
The above objects are realized by a communication system comprising a storage section in which threshold values respectively suitable for the normal receiving mode and the specific receiving mode are registered in advance.
In the communication system, a threshold value to be used for any of receiving modes is obtained with promptness and high accuracy without performing any special calculation as long as proper values are written in advance to the storage section.
A reference threshold value to be used as a threshold value in one of the normal receiving mode and the specific receiving mode, and differences between the reference threshold value and threshold values to be used in respective receiving modes other than the one receiving mode are given in advance. The reference threshold value are used as a threshold value when the identified receiving mode is the one receiving mode, and the sum of the reference threshold value and a difference corresponding to a receiving mode other than the one receiving mode are used as a threshold value when the identified receiving mode is the receiving mode.
In the communication system, threshold values to be used in receiving modes other than the prescribed receiving mode are given as values relative to the reference threshold value to be used in the prescribed receiving mode.
The above objects are achieved by a communication system comprising a storage section in which either or both of a reference threshold value to be used as a threshold value in one of the normal receiving mode and the specific receiving mode and, differences between the reference threshold value and threshold values to be used in respective receiving modes other than the one receiving mode are registered in advance.
In the communication system, a threshold value to be used in any receiving mode is obtained with promptness and high accuracy without performing any special calculation as long as proper difference values are written in advance to the storage section.
The above objects are realized by a communication system where a reference threshold value to be used as a threshold value in one of the normal receiving mode and the specific receiving mode and ratios of threshold values to be used in respective receiving modes other than the one receiving mode to the reference threshold value are given in advance. The reference threshold value are used as a threshold value when the identified receiving mode is the one receiving mode, and the product of the reference threshold value and a ratio corresponding to a receiving mode other than the prescribed receiving mode are used as a threshold value when the identified receiving mode is the receiving mode.
In the communication system, threshold values to be used in receiving modes other than the prescribed receiving mode are given as ratios with respect to the reference threshold value to be used in the prescribed receiving mode.
The above objects are achieved by a communication system comprising a storage section in which either or both of a reference threshold value to be used in one of the normal receiving mode and the specific receiving mode and ratios between the reference threshold value and threshold values to be used in respective receiving modes other than the one receiving mode are registered in advance.
In the communication system, a threshold value to be used in any receiving mode is obtained with promptness and high accuracy without performing any special calculation as long as proper ratios are written in advance to the storage section.
The above objects are achieved by a communication system where either or both of writing and updating of values to be registered in the storage section are performed.
In the communication system, values to be registered in the storage section are written or updated when necessary through man-machine interfacing.
Writing and updating of values to be registered in all or part of the storage sections are performed under a channel control.
In the communication system, values to be registered in the storage section are written or updated every time a predetermined event is recognized during the process of a channel control.
The above objects are further achieved by a communication system comprising a section for performing either or both of forward alignment guard and backward alignment guard in accordance with a judgment result of establishment of frame synchronization. When the identified receiving mode is a certain receiving mode, the section is restricted from operating or results of the forward alignment guard and the backward alignment guard are vitiated.
In the communication system, the forward alignment guard and the backward alignment guard do not function effectively for a frame not including the number of consecutive slots larger than the number of stages of the forward alignment guard and the backward alignment guard.